Analyses of cytoskeletal proteins in the Xenopus and squid nervous system has been facilitated by the production of a panel of monoclonal antibodies (Mabs) against these proteins. In the squid, these Mabs have been used to show that phosphorylation of neurofilaments occurs only in the axon. Analysis of the protein kinase-calcium activated protease-neurofilament complex in the squid giant axon has shown that the protein kinase is similar to type II casein kinase, and that an inhibitor of this kinase is located in the cell bodies in the stellate ganglion. In the Xenopus nervous system the Mabs have allowed for the detection of neuronal-specific cytoskeletal proteins (including neurofilaments) during embryonic development. A Xenopus brain cDNA library is being probed for clones containing neurofilament sequences. A mouse genomic library is being probed for the presence of vasopressin and oxytocin precursor sequences.